Many places along rivers in Wairarapa are good for swimming except after rain, a new Recreational Water Quality report card shows.
The report card from the Greater Wellington Regional Council (GWRC) shows water quality was particularly good last summer due to particularly dry weather.
Last season only one sample of the 289 taken did not meet the guidelines for safe swimming compared with eight sites last year. According to GWRC this is because less rainfall resulted in less contamination being washed off the surrounding catchments into rivers.
The council's senior environmental scientist Summer Greenfield said rainfall washes contamination from surrounding urban and rural land into waterways.
"We encourage people to wait two days after heavy rain before swimming again.
"Nearly three-quarters of sites we monitor in Wairarapa had an overall A or B grade which mean there was a low risk of illness," she said.
The best sea sites for swimming were Castlepoint and Riversdale beaches and the rivers were the Waingawa and Waiohine.
"Unfortunately the warm, dry weather created perfect conditions for toxic algae which was a problem in the Waipoua River. We'll be starting our next summer monitoring programme in December. We'll keep the community continually informed of water quality so they can get out and enjoy their recreational activities safely," Ms Greenfield said.
Despite the report card results the Ruamahanga River has been identified by the Green Party as one of the worst for swimming in the wider Wellington region and earmarked as one of the waterways to be visited by the party's MPs during its Swimmable Rivers campaign later this month.
The Ruamahanga River scored a D rating for swimming at The Cliffs, south of Masterton, in the regional council's report card.
The Green Party's water spokeswoman Catherine Delahunty said the Ruamahanga River's story "is a tragic one".
"It starts out pristine in the Tararua Ranges but by the time it gets to the sea, the water is in a grim state.
"Lots of people are working hard to clean up the river and limit the pollution going into it, but without strong minimum standards from government, many of our worst-off rivers - and the communities who treasure them - will suffer."
Ten rivers said to be under stress from intensive agriculture, silt build-up, sewage, urban contaminants and other pollution will be visited by MPs with Metiria Turei, who has family links to Papawai, and Ms Delahunty inspecting the Ruamahanga River prior to calling a public meeting in Carterton on July 28.